There are various topologies for antennas that are broadband in terms of voltage standing wave ratio (VSWR) and that can be used in various application fields (commercial, military, industrial, . . . ).
Thus, as examples, the topologies in the most widespread use are the following: antennas that are independent of frequency (spiral, log-periodic); and broadband dipoles (elliptical, volume, planar, . . . ). These topologies can be used in the context of making antennas that are directional or that are omnidirectional.
In another form, passband can be increased by means of an added matching network that can incorporate some number of discrete or pseudo-lumped components (capacitors, inductors, resistors, transformers, etc.).
One of the problems associated with using a matching network lies in the physical limitations that arise from making use of components. Thus, such solutions do not in any way make it possible to modify or shape the radiation characteristics of the individual radiating element. Furthermore, a matching network reduces the intrinsic power performance and efficiency of the radiating element. Nevertheless, in spite of certain radiation-shaping properties, the use of the above-mentioned broadband topologies does not make it possible to provide structures that are compatible with all applications.
Thus, with respect to form factor, such antennas need to present dimensions that are close to wave lengths. In addition, in order to obtain omnidirectional coverage, conventional form factors (wire antennas) cannot be satisfied, thereby making it more complicated to integrate beam-conserving antennas in applications of the portable or vehicle type.
With the arrival of new communications standards making use of time-division signals, such antennas also suffer from problems of dispersion relative to the position of the phase center, making it difficult if not impossible to implement such systems.
Nevertheless, several structures have been developed for the purpose of mitigating the above-mentioned problems.
U.S. Pat. No. 6,339,409 discloses an antenna formed by rolling up a single electrically-conductive sheet having the shape of a right-angled triangle.
US patent application No. 2006/0071873 describes an antenna as mentioned above connected to a ground-forming disk.
U.S. Pat. No. 4,527,163 describes a monostrip antenna having an outer element formed by a sheet cut out to present a Y-shape.